The present invention relates to a device for determining the position of a vehicle at an airport according to the preamble of claim 1. The device according to the present invention is particularly intended for defining the position of aircraft on the runway system (taxiways, take-off and landing runways and platforms) of the airport. The position of other vehicles can also be determined.
European patent application EP-A-0 744 630 describes an airport surface monitoring and runway incursion warning system, in which a position of an aircraft is detected using a transmitter on board (from the transponder system) co-operating with a number of modules in radar sensor units which are disposed adjacent to a runway.
A device of this type for determining a position of a vehicle, such as an aircraft, is known and is already used at a number of airports. This known system makes use of a multilateration technique, which is based on the calculation of a position through the measurement, at various locations, of the time of reception of a signal, such as a transponder signal, transmitted by an aircraft or vehicle. In order to define a two-dimensional position, at least three receivers are required at separate locations. For the sake of operational reliability and redundancy, more than three receivers will generally be used at an airport. A transponder already available in the aircraft is generally used for position determination.
This multilateration technique has a number of disadvantages. Firstly, the signal needs to be transmitted by the aircraft whenever the aircraft is located on the ground, during manoeuvres at the airport. This requires an adaptation of the procedures currently implemented at airports and, in some cases, technical adaptation to aircraft systems. Since additional transponder signals are transmitted with the known system, there is a greater risk of interference to ground systems (such as radar) and aircraft systems (such as TCAS equipment, which serves to prevent mid-air collisions). Furthermore, the multilateration technique is sensitive to multipath interference of the transmitted signals, which may result in incorrect positions. Multipath interference is caused in particular by reflection on large (metal) objects, such as the ubiquitous airport hangars. Finally, there is the risk that, by leaving transponders switched on, xe2x80x98fruitingxe2x80x99 occurs in the receiving installations, since many aircraft are located at roughly the same distance from the receiving installations. This occurs in particular in the case of incorrectly functioning transponders, or transponders of an older type (Mode A/Mode C transponders).
Currently, the devices based on multilateration do not (yet) comply with international regulations relating to the required accuracy and availability of devices for determining the position of aircraft on airfields.
The object of the present invention is therefore to provide a device for determining a position of a vehicle, such as an aircraft, at an airport which does not reveal the aforementioned disadvantages and which can be used under all conditions, in particular under conditions of poor visibility.
This object is achieved with a device of the type defined by the technical features of claim 1.
The advantage of the device according to the present invention is that position determination of vehicles, such as aircraft, is possible at an airport, with sufficient accuracy for a traffic controller at an airport. By positioning the sensors at regular intervals, it is possible to track a vehicle, such as an aircraft. The reception characteristics of the sensors can thereby be adapted in such a way that no multipath interference occurs. According to international regulations, all (larger) aircraft are fitted with a radio altimeter, whereby the use of the device according to the present invention requires no adaptation of the aircraft or the operational procedures of the aircraft. This makes the implementation of the present device simple and cost-effective. Since the antennas of radio altimeters in aircraft are normally located on the underside of the aircraft, the extent of the area in which the radio signal is to be received will be limited. As a result, the radio signal will be received at a given moment by only one or a few of the plurality of sensors, whereby unambiguous and interference-free detection of a vehicle can take place.
In one embodiment of the present invention, the plurality of sensors are positioned in light points of runway lighting provided at the airport. The position determination of aircraft and other vehicles is referred in this embodiment to the runway lighting already provided at the airport, such as the central lighting in taxiways and the direction lighting on platforms. Making use of existing runway lighting to position the sensors offers the advantage that no additional infrastructure needs to be set up.
In a preferred embodiment of the present invention, at least one sensor of the plurality of sensors is provided with a direction-sensitive antenna. This can supply additional information which may be useful in determining the position of a vehicle, such as an aircraft, particularly if the radio signal is received at a given moment by more than one sensor. The at least one sensor is furthermore preferably provided with a signal-processing unit to process the signal detected by the at least one sensor. This makes it possible to (pre-) process the received signals in the sensor itself, thereby enabling simpler or more efficient data communication, for example via power supply lines of the light points of the runway lighting.
In one embodiment, the present device furthermore comprises a central processing device to collate, process and reproduce data originating from the plurality of sensors. The central processing device is preferably arranged to allocate an identifier to data originating from the plurality of sensors. This allocation may, for example, be based on the frequency characteristic of the at least one radio signal. These characteristics may be one or more of the following: strength, direction, frequency (furthermore all as a function of time), frequency-modulation characteristics and frequency difference in the case of an aircraft which is equipped with a plurality of radio altimeters which transmit a different signal.
The central processing device is furthermore preferably provided with warning means to generate a warning if the detected position of the vehicle is located outside a predefined area of the airport which is permitted to the vehicle. The permitted area for an aircraft may, for example, comprise a route via defined taxiways, parts of platforms and (parts of) a take-off or landing runway. Furthermore, the central processing device may be arranged to predict the further position of the vehicle and to generate a warning if, on the basis of the prediction, a possible conflict will occur between a plurality of vehicles. With the present device, the traffic controller is therefore warned if an aircraft or other vehicle is located in an unauthorised area or if a collision between aircraft and/or other vehicles is imminent.
A further aspect of the invention relates to a transmitting device for generating a radio signal, in which the radio signal can be detected by the plurality of sensors which are contained in the device according to the first aspect of the invention. This transmitting device is required, for example, so that vehicles which are not equipped with a radio altimeter or other transmitting device can be rendered detectable by means of the present device.